Process for the production of cellulose by decomposition of vegetable fibers



Patented Mar. 12, 1929.

UNITED STATES A I 1,105,424 PATENT OFFICE.

OTTO CARL STRECKEB, OF DARMSTADT, GERMANY.

PROCESS FOR THE PRODUCTION OF CELLULOSE BY DECOMPOSITION OF VEGETABLE FIBERS.

No Drawing. Application filed February 25, 1927, Serial No. 171,060, and in Germany September 30, 1924.

. by the decomposition of vegetable fibers such C H OCl or phenol, (1 H for example as red pine wood, straw and the like, it has generally been the custom to boil the fibrous materialwith alkaline or acid liquids. In the former case the yields are poor and the cellulose obtained is often diflicult to bleach, whilst the use of the latter liquids is attended with difliculties owing to their chemical action on the apparatus. In both cases waste liquors are obtained which can not or only with difiiculty be further employed. It has been customary to concentrate the waste liquors and to burn themv or to empty them into rivers, both of which courses are, however, wasteful because these liquors contain more than half of the raw material.

In addition to the liquids mentioned it has also been proposed to employ other liquids of neutral or slightly acid reaction, such for example as e ichlorohydrin,

These substances however have not come into general use owing to their high cost.

For some time grasses have been decomposed by means of chlorine in the gaseous form or by means of chlorine-containing liquids which has generally been done in combin ation with other processes, but this decomposition process involves a troublesome method of working, requires chlorine resisting apparatus, and could so far only be applied to grasses.

According to the new process forming the subject of the present invention the formation of waste liquors of such a kind that their further treatment on an industrial basis is not economic is avoided. The process enables all the component parts of the vegetable fibers to be utilized and yields a cellulose which without subsequent treatment is of a specially high grade. The yield is almost equal to the actual cellulose content of the vegetable fibers treated. The liquids used for boiling (hereinafter referred to as boiling lyes) do not attack iron. The reacting chemicals consist of neutral salts which have no action at all or only a slight action on cellulose. More over that portion of the vegetable fibers which is dissolved is not decomposed to a great extent and the number of the decomposition products is relatively small and they are moreover easily utilizable. The cellulose obtained is practlcally free from the other component parts of the vegetable fibers.

Owing to the properties of the boiling lyes utilized according to the invention the most.

varied kinds of vegetable fibers such for example as those of red pine wood, beech wood, bamboo, straw and also resinous woods, such for example as Scotch fir, can be easily'treats ed so as to yield high grade cellulose.

According to the invention boiling lyes are utilized which necessarily contain one or more soluble oxy-compounds of the isocyclic series, in which at least one hydrogen atom of the oxy roup has been replaced by a metal, and I pre er to use for this purpose metals of the alkali group, certain of the alkaline earth metals, and metals of the magnesium group.

The following oxy-compounds of the isocyclic series may be utilized, these being given by Way of example only and their international or so called Geneva designations being added in brackets 1. Phenols, for example, phenol (oxybenzene) C H O or cresol (oxytoluene) (LH O;

2. Alcohol phenols for exam. le, phenol alcohol (oxybenzyl alcohol or ioxymethyl benzene) C H O C G cl 0 h e x e n 01 (tetrahydrophenol) 6 10 3 4. Hydrated phenols, for example cyclohexanol (hexahydrophenol) C H O;

5. Naphthols for exam le, alpha naphthol (oxynaphthalene) O l-I 8;

6. Hydrated naphthols for example oxynaphthalene tetrahydride C H O or oxynaphthalene decahydride 0 E 0;

7. Methylcyclohexanol (hexahydroxytoluene) C,H, O;

8. Polyoxides for example resorcin (dioxybenzene) C H O 9. Oxysulfones for example sulfonoxybenzene C H O SO 10. Sulfoor carbo-acids of the above substances and the salts of these acids including also metal salts which decompose on heating and form on the one hand oxycompounds and on the other hand sulphites or carbonates, such as for example oxybenezene sulfonic acid Q ILOHSOJ-I, or oxybenezene carbonic acid O.,H,OHCO H and their sodium salts O ILONaSO Na or O H ONaCO Na 11. Functional derivatives of phenol and its homologuesand especially such derivatives as contain alkyl or aryl groups winch are split off on fusing with alkali provided that such substances contain one or more oxythe case of dioxycompounds one hydrogen.

atom and in the case of polyoxycompounds several hydrogen atoms, may be replaced by alkyl, aryl or acetyl groups provided that at least one ox group can be provided with a metallic cathion. The molecular constitution of these substances is not material and a plurality of them can be utilized mixed together, thus for example, ortho-, meta-, paracresol can be used either alone or mixed together.

The metals mentioned combine as cathions with the oxycompounds referred to as anions to form salt-like compounds, for example, phenolates or phenol alcoholates. The anions can be added to the vegetable fibers either separately or combined in the form of salts and either cold or warm.

For the purpose'of decomposition the substances named are preferably utilized in the form of solutions or as permanent emulsions, that is to say, emulsions that will not separate. If the production thereof should be difficult the precipitation of the solutions or the separation of the emulsions may be prevented in any known and/or suitable manner by the addition of certain substances. For this purpose, for example, soaps of castor oil, cyclohexanol C H O and salts of humic acid may be found suitable and these added substances may be so selected as either to increase, reduce or be without effect on the decomposing action of the boiling lye on the vegetable fibers. In every case it is immaterial whether the ions or salts are brought into contact with the vegetable fibers in the form of solutions or emulsions or undissolved in the presence of the solvent or emulsifying agent, and the anion or cathion component may also be present dissolved in slight excess.

For the purpose of assisting a more rapid penetration of the vegetable fibers there may I be added alkaline, neutral or slightly acid salts, for instance trisodium phosphate Na ,PO,, weak acids with basic, slightly alkaline, neutral or acid reaction, metallic bases, aliphatic or aromatic alcohols, phenol alcohol, as well as their homologues and functional derivatives, the latter being phenol derivatives the constitution of which is unknown.

For a similar purpose catalytically acting substances such as barium peroxide BaO may be used.

The time of treatment, i. e. boiling'time, depends on the nature and condition of the vegetable fibers to be decomposed, on the nature and strength of the boiling lye, the movement imparted to the boiling lye, or to the mass to be treated, and on the temperature and pressure employed. The decomposition can be materially expedited if before boiling the air which clings to and is contained by the fibers is removed, for example by application of reduced pressure or by replacement by other gases.

Just as most chemical reactions may be expedited by increase of temperature, pressure or both, so the decomposition of the vegetable fibers can be more rapidly efiected according to the new process by the employment of higher temperatures or pressures. In the event of this involving any danger of deterioration to the boiling lyes for example as a result of oxidation and of their consequently losing their effect this can be guarded against by adding substances of neutral or alkaline reaction and reducing effect to theboiling lye either before commencing the process or during the boiling. As examples of such substances I refer to neutral salts of sulphurous acid such as Na SO salts of formic acid, for example CHCO Na, alkaline salts of tartaric acid for example C O H Na and malic acid C O H Na sodium phenyl sulfonate C H O SNa, their homologues and substitution products, stannous oxide and the like.

lVhen vegetable fibers are treated with the boiling lyes described the cathionic portion of the lye very rapidly disappears from its compound and it can be shown that acids are formed from the vegetable fibers with which it combines to form salts. If for example the boiling lye consists of an aqueous solution of sodium phenolate C H ON a roduced by the reaction of caustic soda Na H and phenol (oxybenzene) C HO in which the latter forms the anion and the former the cathion then a portion of the alkali is used up in combining with the acid and phenol is set free. The boiling lye loses some of its effect due to chemical decomposition and moreover has an undesired effect on the vegetable fibers.

In order to prevent the cathion being completcl y used up a metal compound is, according to the invention, added to the boiling lye during the boiling operation, the quantity thereof being sufficient approximately to maintain the original alkali content and to prevent the acids from decomposing the lye. As examples of such metal compounds there may be mentioned some of the alkaline bases or 211- tions the quantities of acid will then form substantial quantities of neutral salts and these remain present as such even in strong concentrations and generally they do not adversely effect the decomposition of the fibers.

Moreover new substances areformed during the boiling operation which substances are capable of combining with the cathion of the boiling lye, that is to say, of supplementing and increasing or even taking the place of the anion of the original boiling lye i. e.phenol in the example; mentioned C H O. The anions of' the boiling lye can thus be produced from the vegetable fibers themselves during the progress of the boiling operation owing to their being formed out of certain components of the same. The latter decompose during further treatment with the added cathion substances where desirable in the presence of added catalysts and boiling lyes in accordance with the invention are formed. This react-ion already commences during the decomposition of the vegetable fibers.

Experience has shown that the boiling lye can be reused in a continuous boiling operation without loss of effect. At the conclusion of any boiling operation only a small portion of the lye need be removed. Thereupon the lye is heated further and cathion material and solvent or emulsifying material is added when, as already stated, new sub-' stances are formed in place of the phenolate C H ONa which substances correspond to the phenol of the example mentioned in the original boiling lye and replacethe portion removed. This supplementing of, addition to or substitution of the original anions present in the boiling lye is of the greatest practical importance. because the first cost of the commerc ally obtainable anion mater al is relatively high and the very large quantities of phenolates which are necessary could not be obtained elsewhere. 7

The whole of this addition process should be analytically controlled.

Furthermore the waste liquors from previous boilings'can be utilized for obtaining the anions therefrom either separately or in combination with cathions for use in the I preparation of fresh boiling lyes.

Owing to the fact that 'in this manner new substances are obtained out of the fibers the total amount reclaimed is suflicient not .only for the compensation of undesirable losses but the proof supplementing the boiling lye. of making,

continuous use of the heat it holds. At the conclusion of the treatment there is no need to release the pressure on the boilinglye and let it 011' thus losing the heat units it contains. Onthe contrary it may be drawn off with retention of the tei'nperature and pressure partially reduced in quantity and the requisite amount of cathion and solvent or emulsifying agent-added and straightway brought up to strength by anion forma tion without further heating, or at any rate wit-h less heating. It is then suitable for fu ther use without any deliberate cooling. The solvent-or emulsifying medium-can also be brought up to the necessary quantity after the anion side has been completed.

The process can be even more economically (carried out in"'a boiling vessel capable of being continuously charged and unloaded with vegetable fiber and cellulose respectively, or in a series of boilers connected together into a battery. If for exam le, the

stream in a continuously chargeable and unloadable boiler, it can be reclaimed continuously after drawing off from the boiler and re-used again without cooling. The use of boilers connected up. one behind the other makes possible the use of fresh lye, by supplementing between the boilers, up to a certain maximum concentration or in similar manner a continuous enriching from boiler to boiler of a primarily weak boiling liquor.

It is not necessary always to use only an exact chemically determined anion. On the other hand however, it is necessary that the anion or the anions should be of phenol character and be chemically combined with a cathion.

For the preparation of the boiling lye a sodium salt of an aromatic phenol, e. g. so-

I ing pumping.

Neutral sodium sulphite Na SO can also be added as reducing agent in which case 10 to- 20 parts of the salt containing water of crystallization should be used. 1

The amount of the boiling lye should be sufficientto about cover the vegetable fibers in the boiler. In the following are given a few examples of the new process.

1. 160 parts of straw or Esparto grass are warmed for a considerable time to a temperature of to 100 C. with 1200 parts of lye of the specified strength in an open vessel having a double perforated bottom and a per foratcd cover below the top rim of the vessel. The lye is circulated by a pump arranged outside the boiler. The composition of the lye is maintained at about the same titer as at the beginning by admixture of alkali.

The decomposition will be completed when the cellulose on examination is found to split up easily into fibers. e

2. 160 parts of straw or Esparto grass are warmed with 1200 parts of lye of specified strength in a closed boiler adapted to circulate the lye. The temperature is very slowly raised during about 4 hours to 140 C. and then maintained for 4-0 hours at 150 to 160 C. The replacing of the alkali can be accomplished after determination by titration outside the boiling vessel. The addition can then be made in a solid or liquid form dur- 3. 220 parts of wood e. g. red pin wood, are heated with 1300 parts of lye of the specified strength slowly during 5-6 hours to 120 C. in a boiler adapted to circulate the lye. During this time-additions of alkali to the extent of about 16 to 18% of the weight of wood are madeI The temperature is then quickly raised to 180 C. and this temperature maintained for generally about 4.6 hours.

In order to avoid oxidation of the boiling lye 20 parts of crystallized sodium sulphite Na So or any alkali sulphite may be added, keeping the relative amount of lye the same, or other sulphites' may be added which do not interfere with the reaction.

4. The relative amounts and method of working are the same as in 3, except that instead of sodium hydroxide, trisodium phosphate (Na POQ is added. The alkalinity will not suffer by this because one of the three sodium atoms in the phosphoric acid salt is split ofi? by the tertiary alcohol and in this way phenolate is again formed, whilst disodium phosphate Na HPO reacts alkaline. The amount is then 44% of the weight of the wood, and the 18% of sodium hydroxidecan also'be only partly replaced by an aliquot part of phosphate. Similarly for example. tri potassium phosphate K PO can also be used.

Ammonia and ammoniacal derivatives are formed in the boiling of grasses. Decomposition products of plant albumen are also followed by a 0.2% hydrdchloric acid solu- 7 tion is recommended.

The waste liquor after letting as a part and dilution with water and addition of alkali is regenerated again by boiling until the prescribed strength of 40 perthousancLof phenol combined sodium hydroxide is approximately attained. Care must be taken to find out that the sodium hydroxide is completely combined with phenol for which special testing methods are available.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is 1. A process for the production of cellulose which comprises decomposing vegetable fibers by boiling the said fibers in a solution comprising a metalliccompound of a soluable hydroxy-compound .of the iso-cyclic series.

2. A process for the production of cellulose which comprises digesting vegetable fibers in a hot water solution of a soluble alkaline metal derivative of a soluble hydroxy-compound of the iso-cylic series.

3. A process for the production of cellulosev which comprises digesting vegetable fibers in a hot aqueous solution of a metallic derivative of a water-soluble. hydroxy-compound of the iso-cyclic series in the presence of a phenolic body and an acidic derivative having the property of yielding a hydroxycompound.

4. A process according to claim 1 wherein substances are added-to the boiling solution to cause the formation of stable solutions or permanent emulsions.

5. A process according to claim 1 wherein the ions are brought together with the vegetable fibers. I

6. A process according to claim 1 characterized b the feature that a metal compound is a ded as cathion during the boiling step and in sufficient quantity to convert the metallic compound into a salt which will not injure the cellulose and wherein the acids split off from the vegetable fibers are utilized tohinder the decomposition of the boiling lyes by the acids formed during boiling.

7. A process according to. claim 1 characterized by the feature that the necessary. anions for the preparation of the boiling solution are obtained from the vegetable fibers tion.

8'. A process according to claim 1 wherein a ortion of the boiling solution is separated a ter each use and is brought up to the concentration and v uantity necessary for the next boiling by t e sole addition of cathion and solvent agent and heating.

9. A process according to claim 1 wherein the anions in the free state or combined in the form of a compound with the cathion are separated and recovered out of the constituents of the vegetable fiber in the waste liquor after having been used and are used in the preparation of a fresh boiling solution.

10. A process for the production of cellulose which comprises decomposing vegetable fibers by boiling the said fibers in a solution comprising a metallic compound of a soluble hydroxy-compound of the iso-cylic series, and adding to the boiling solution a hydrolyzable salt and an alcohol.

11. A process for the productionof cellulose which comprises decomposing vegetable fibers in a solution comprising a metallic derivative of'a soluble hydroxy-compound of the iso-cyclic series, and adding to the boiling of the iso-cyclic series, and adding to the 1 boiling solution a hydrolyzable salt, an alcohol, a catalyst, and a reducing agent.

13. A'process for the production of cellulose which comprises decomposing vegetable fibers in a solution comprising a metallic derivative of a soluble hydroxy-compound, and adding thereto a metallic compound capable of forming a metallic cathion in the boiling solution.

14. A process for the production of cellulose which comprises decomposing vegetable fibers in a solution comprising a metallic com ound of a soluble hydroxy-compound of t e iso-cyclic series, boiling ,the fibers in the said solution, and recovering the solution for re-use.

OTTO CARL STRECKER. 

